When we don't get enough sleep, our bodies age more quickly, according to Dr. Ray Sahelian, author of Melatonin. Quality sleep is also essential to good health because deep sleep rejuvenates the immune system.

Many of us mistakenly believe that as we age, our sleep quality declines. In fact, how well you sleep depends on your habits and lifestyle: If you eat a good diet, exercise and manage stress properly, you can sleep like a baby well into your 80s or 90s.

But the demands of our fast-paced, complex lives have affected our snooze time, and millions of Americans don't get enough sleep.

"It used to be considered a status quality if you could get by with less sleep," says Keri Brenner co-author of Sleep Disorders. "But sleep is when the body repairs itself. Without enough sleep, the muscles, organs and cells don't have enough time to repair from the day."

We can improve our chances for a good night's sleep. According to Brenner, some of the most common causes of sleep disturbance include:

Poor Diet and Food Allergies

Caffeine, sugar and spicy foods all contribute to sleep disturbances. Caffeine stays in the body for up to 20 hours, and sugar causes an emergency stress reaction in the blood that can disrupt your sleep. And alcohol, although it may help you fall asleep, disrupts deep sleep states and reduces sleep time.

Disrupted Circadian Rhythms

Circadian rhythms, the biological clock that tells the body when to eat or sleep, can also affect the quality of your zzz's. Limited exposure to natural light, pharmaceutical drugs, electromagnetic fields, stress, travel or shift work-all can impair the pineal gland's ability to produce melatonin, a natural hormone that promotes sleep. Reprogramming your body clock to improve sleep is possible through diet changes, exercise, stress management and melatonin supplementation.

If you have trouble sleeping, Sahelian recommends 0.3 to 0.5 milligrams of melatonin once or twice a week an hour or two before bed. But beware that excessive amounts can have the opposite effect: More than 1 or 2 milligrams of melatonin can make you feel groggy the next day.